Line the base and sides of a loaf tin with baking paper. Place the caster sugar and lemon zest into the bowl of an electric mixer fitted with a beater and mix together for 2 minutes so that the lemon infuses the sugar. Next, add in the flour  (reserve 1 tbsp flour)and baking powder and mix. Next, add in the softened butter 1/3 at a time till the mixture looks like a crumble. Beat in the eggs, one at a time followed by the vanilla, lemon juice and milk. Mix the reserved 1 tbsp flour into the frozen blueberries and mix into the cake. Spoon the cake batter into the prepared tin and bake at 180` for approximately 50-60 minutes. When cooled down, mix together the icing sugar with enough lemon juice to make a glaze icing. Spread over the loaf and decorate the top with fresh blueberries and edible flowers.